The word was used as early as 1868, according to the OED, to refer to a piece of equipment used in glassmaking. Not long after that, nautical and Navy slang gave it another meaning. From an 1886 book: “Then the names of all the other things on board a ship! I don’t know half of them yet; even the sailors forget at times, and if the exact name of anything they want happens to slip from their memory, they call it a chicken-fixing, or a gadjet, or a gill-guy, or a timmey-noggy, or a wim-wom…”
It wasn’t until World War I that ”gadget” adopted the meaning (and spelling) we associate with it today—in the OED’s words, “a (small) mechanical or electronic device, esp. one regarded as ingenious or novel.” At first it was used in a specifically military context. Rudyard Kipling wrote in The New Army (1915): “They have installed decent cooking ranges and gas, and the men have already made themselves all sorts of handy little labour-saving gadgets.”
It quickly spread to other contexts. Correspondent H. Tapley-Soper wrote to Notes and Queries in 1918: “I have … frequently heard [‘gadget’] applied by motor-cycle friends to the collection of fitments to be seen on motor cycles. ‘His handle-bars are smothered in gadgets’ refers to such things as speedometers, mirrors, levers, badges, mascots, &c., attached to the steering handles.”
And it quickly spread to the United States. A 1919 New York Times article about a transatlantic flight noted, “It was no unusual sight to see [the pilot], tools in hand, busily fitting some ‘gadget’…”
Within ten years, Americans were using it more than Britons, according to Ngram Viewer:
That spike in the ‘30s and ‘40s is presumably what caused The New Yorker, under the editorship of William Shawn, to actually ban “gadget” from the magazine’s pages, along with a remarkable number of other words. Two editors at the magazine, John Bennet and Nancy Franklin, once composed a sentence to try to help them remember all of the things they had to eliminate or find replacements for: “Intrigued by the massive smarts of the balding, feisty, prestigious, workaholic tycoon, Tom Wolfe promptly spat on the quality photo above the urinal and tried to locate his gadget.” (They left out “gotten.”)
notoneoffbritishisms.com 
Online Etymology Dictionary says: ‘perhaps from French gâchette “catch-piece of a mechanism” (15c.), diminutive of gâche “staple of a lock.” The page also says that the US near-equivalent ‘gizmo’ also originated in ‘Marine and Navy usage’, but later, around 1942 : https://www.etymonline.com/word/gizmo
My ex-RAF friends have two or three other near-equivalents; the only one I can recall is ‘dooberry’, which sounds to me more American than British.
Chambers gives that as doobrey/doobrie.
I’d never seen it written, Paul. Did you know that ‘nickel and dime’ can be a verb? Nor did I, till I did last night’s Phrazle (nickel and dimed). Still no whiff of a non-American phrase there.
Don’t even know what “Phrazle” is. 🙂
It’s a ‘work out the phrase’ puzzle Paul, where you enter likely words, get marked for them, then guess again. Here you are: https://solitaired.com/phrazle
I usually solve it in 2 or 3 guesses, except when it’s a particularly obscure American phrase. Tonight’s solution was ‘short end of the stick’, which foxed me and the missus (we compete). We each assumed that as ‘wrong end of the stick’ didn’t fit, the first word had to be ‘right’.
I try to do at least one cryptic crossword daily, plus an online killer sudoku. I don’t think I have time for another daily puzzle. 🙂
if your gadget is on the fritz, tweak it with a wanking spanner or hang it from a couple of skyhooks, and it’ll all be hunk-dory